The present invention relates to a justification system for use in a printer employing a continuous form, and more particularly to a justification system for correcting undesirable displacement of a predetermined printing segment defined on a continuous form in its longitudinal direction.
Conventionally, there is known an image recording device that utilizes a so-called electrophotographic system in which a surface of a photoconductive drum is exposed to light to form a latent image on the drum surface. Toner is then applied to the latent image to develop the image, and the developed image is transferred onto a recording sheet material and fixed by a fixing unit. Such an image recording device is usually employed in a copying machine. In recent years, however, such image recording devices have been employed in printers and the like for printing the output from a computer.
In a copying machine, in general, cut sheets are used as the recording sheet materials. In a printer, however, it is desirable to use a continuous recording form as the recording medium. Such a form is identical with that used in a conventional line-printer. The continuous recording form is a folded continuous recording form (hereinafter referred to simply as "continuous form") called a fan-folded form which has sprocket holes formed along both side edge portions thereof. A perforation is provided at each of the folded sheet sections to define a printing segment between successive perforations and to enable the sheet sections to be easily separated from each other. Horizontal rules are marked at predetermined intervals in a longitudinal direction between the perforations with a predetermined positional relationship in respect to the sprocket holes.
However, in an electrophotographic printer a continuous form to which an unfixed toner image is applied is clamped and passed between a pair of rotating fixing rolls so that the toner image is fixed onto the continuous form. Accordingly the continuous form is usually driven by the rotation travel of the fixing rolls.
When the continuous form is transported by the fixing rolls, several problem might arise. For example, the continuous form that is clamped between the fixing roll can skew or meander because of various factors. If such skewing or meandering occurs, a defective fixing of the image and a defective transportion of the continuous form occurs. In view of such problems, an arrangement has been proposed, by the present assignee (see U.S. Ser. No. 177352 filed on 1st Apr., 1988), in which a direction-regulating feed mechanism is provided for a applying a tension to a portion of the continuous form that extends between the photoconductive drum and the fixing roll pair, so as to uniformize the state of the continuous form to be bitten into the nip between the pair of fixing rolls. With such a direction-regulating feed mechanism, it is possible to prevent skewing or meandering of the continuous form, and to automatically restore the continuous form to the regular position even if such skewing or meandering occurs.
In the printer employing the continuous form described above, there still remains another problem. Due to a misalignment between the continuous form and the direction-regulating feed mechanism caused when setting the former to the latter and/or to the expansion or contraction of the continuous form caused by humidity changes and so on, the associated area of circumferential surface of the photoconductive drum is shifted out of position with respect to the corresponding area of the continuous form. Thus, the printing position slips away from the rules on the continuous form. The continuous printing accumulates the displacements between the circumferential surface of the photoconductive drum and the continuous form with the result that the rules are meaningless. Also printing is executed on a non-printing area proximate each perforation on the continuous form which permits the form to be cut into separate sheets after printing.